It is well known that many petroleum stocks contain sulfur and nitrogen. It is desirable for many applications of the petroleum stock itself or of the products made from it that these be removed. This is an operation requiring a catalyst, and one in common use is an alumina base containing cobaltia and molybdena.
From Shiroto et al., U.S. Pat. No. 4,422,960, it is known that catalysts for hydrotreatment of heavy hydrocarbon oils can be efficiently prepared by coprecipitating oxides of Groups II, III and IV of the Periodic Table in the form of hydrosols. It is further known that such hydrosols can be increased in size to form hydrogels by alternating increasing then decreasing the pH, with base and then with acid, and it is reported to be beneficial to repeat this so-called "pH swing" from 2 to 50 times. The larger hydrogels are then dried and calcined, e.g., at 300.degree. C. maximum to produce catalyst supports. Such supports are then converted into catalysts by impregnation with a minor proportion of a catalytic metal or compound, such as from Groups IVB, VIB, VIII AND IB of the Periodic Table, illustratively, copper, chromium, cobalt, nickel, molybdenum, mixtures of any of them, and the like. The disclosed process of the Shiroto patent has several drawbacks, the primary ones being that the porosity of the catalyst supports is not as high as would appear to be optimum and, especially when salts are used to form the hydrogel, there is a tendency to carry through anionic impurities which can later react with hydrogen to form corrosive substances.
Mikovsky et al., U.S. Pat. Nos. 4,128,505 and 4,186,080, describe titania and zirconia catalyst supports made by coprecipitating, without pH control, the corresponding metal salts, impregnating them with catalytic metals and using them to hydrotreat oils. Because calcining is done in dry air at 1000.degree. F. (538.degree. C.), the Mikovsky process has the drawbacks of producing less than optimum surface area, low pore diameter, and also contamination by anions.
Wakabayashi et al., U.S. Pat. No. 4,248,852, makes an alumina catalyst by precipitating an aluminum hydroxide hydrogel and making it larger and more porous by the pH swing technique. The material is then dried and calcined. Such material will contain anionic impurities and will have less than optimum pore size or surface area, or both.
Other prior art does not appear to disclose catalysts or catalyst supports made exclusively from titania-zirconia or titania-zirconia-alumina, or the use of such supports containing cobaltia and molybdena or other metal oxides or sulfides in hydrotreating reactions. U.S. Pat. No. 3,159,588 does disclose a catalyst containing various combinations of titania and zirconia, but it is essential to the composition that silica be present therein. There is no disclosure in U.S. Pat. No. 3,159,588 of the presence of molybdena or cobaltia. U.S. Pat. No. 2,597,889, U.S. Pat. No. 3,137,658 and U.S. Pat. No. 3,887,494 teach compositions of silica-titania, some containing other metals, in hydrocarbon conversion reactions. U.S. Pat, No. 3,264,227 teaches the manufacture of a silica-zirconia-alumina catalyst useful in hydrocarbon conversion reactions.
U.S. Pat. No. 3,278,421is concerned with refractory inorganic oxides comprising alumina, titania and zirconia, among others which may contain certain metallic components. There is, however, no disclosure of the particular catalyst of the present invention.
U.S. Pat. No. 3,546,103 teaches hydrodesulfurization with a catalyst of cobalt and molybdenum on an alumina base. It has now been discovered that when binary oxidic catalytic support materials are prepared by a pH swing or control pH technique, followed by calcination within a specific temperature range, a material will result with much higher than expected porosity and surface area with less than readily detectable levels of anions. Such products are of substantial utility as catalyst supports, and with impregnation by metal compounds, as catalysts and absorbent materials generally.